Snow Ghosts from Whitefish Mountain looking out towards Glacier National Park (Photo by Rick and Susie Graetz)
One might think these trees have been taken over by encrusted snow, while others erroneously call the coating hoar frost. The truth is that the cover is heavy accumulations of super-cooled water droplets called rime.
During periods of extreme cold, rime from hydrothermal mist accumulates on the branches of trees. When combined with falling snow, trees take on an eerie appearance and are known as “snow ghosts.” Even though the fog and mist caught up in the mountains is at or bellow freezing temperatures, they are made of masses of suspended water droplets.
These super-cooled water droplets can exist in a liquid state between 32 and -40 degrees because they lack freezing nuclei. These droplets freeze however, when they encounter ridge top and summit obstacles - like trees, lift towers, and buildings.
University of Montana's Department of Geography